Comparison of the chemical and biochemical composition of thirteen muscles of the rat after dietary protein restriction

The objective of this study was to determine whether the chemical and biochemical changes induced by muscle wasting caused by dietary protein restriction are different in various skeletal muscles. Rats were fasted for 3 d and then fed on a 10 g protein/kg diet for 21d. Thirteen muscles from the trunk, forelimb, and hind-limb regions were analysed for muscle weight, and the content of water, fat, cellular and extracellular protein, DNA and RNA. Results were compared to values for an `initial' control group killed at the start of the experiment. Weight loss was greatest in trunk muscles and least in the distal forelimb muscles. Water content decreased in most muscles, but increased in three forelimb muscles. A significant loss of lipid was found in the gastroenemius, while the biceps brachii gained lipid. Changes in lipid content of the muscles did not form a distinctive pattern. All muscles except the distal forelimb muscles lost a significant amount of cellular protein, while all muscles except the diaphragm gained extracellular protein. DNA content was unchanged in all muscles. The value for cellular protein: DNA was significantly reduced in the rectus abdominis and the diaphragm. A significant loss of RNA was found in all muscles; the percentage change was greatest in trunk muscle and least in the distal forelimb muscles. The values for RNA: protein and RNA: DNA were significantly lower in all muscles except two distal forelimb muscles. With the exception of the water and lipid content of the muscles, the directions of the changes in the experimental animals were the same for all muscles. The results suggested, however, that the magnitude of changes in certain chemical and biochemical indices of composition may depend to some extent on the anatomical location of the muscle: trunk muscles tended to show the greatest percentage change, while the distal forelimbs changed the least.(AU)

A comparison of the response of thirteen muscles in the rat to dietary restriction

Information derived from a sample of a particular muscle or the entire muscle is often assumed to be characteristic of skeletal muscle in general. There has been little experimental work designed to validate this assumption which has important implications in clinical situations such as severe protein-energy malnutrition in which gross muscle wasting is a characteristic feature. This project was designed to gain information on the changes that take place in a number of muscles in the rat exhibiting severe muscle wasting following dietary deprivation. Eight male albino rats aged 5 weeks and weighing 100g were starved for 33 days and then fed a 1 percent protein diet for 20-22 days. Control animals were albino male rats of the same initial age and body weight. The 13 muscles examined were those of the trunk (rectus abdominis, diaphragm and psoas), thigh (gluteus), hind-limb (quadriceps, tibialis anterior, gastrocnemius and soleus), and fore-limb (Triceps, biceps, brachialis, Flexor carpi radialis and Extensor carpi ulnaris). Estimations on the whole muscle were made of wet weight, dry weight, fat free dry weight, cellular protein, extracellular protein, DNA and RNA. The results showed that the muscles of the experimental animals underwent similar compositional changes in response to the dietary restriction. The changes of four small fore-limb muscle were not characteristic at times. Overall the muscles lost 19 percent wet weight, 17 percent dry weight and 18 percent fat free dry weight. The total water content decreased by approximately 2 percent, cellular protein by 20 percent and total muscle RNA by 44 percent. Extracellular protein increased by 35 percent. There was no significant difference in the total DNA and fat content of nearly all the muscles of control and experimental animals. Although the muscles responded similarly to the dietary treatment the extent of change varied. Caution must be exercised when extrapolating these changes to the entire musculature (Summary)